Surgical scalpels are finger-held in a manner similar to a marking instrument and must be comfortable for the surgeon or craftsman as well as being amenable to fine control. To this extent, it is important that they can be held easily and that they allow the surgeon or other artisan to control the depth and extent of cut both into and along the skin. Scalpels are known having a retractable or non-retractable blade and a depth gauge that adjusts the extent to which the blade protrudes from a body portion. However, the present invention relates principally to a surgical scalpel comprising a reusable handle having a tang at one end on which a replaceable slotted blade is mounted. The blade is discarded after use while the handle may be either disposable or intended for repeated use.
Hand held instruments such as scalpels and writing instruments typically have an elongated handle supporting at a tip a working portion that may be, for example, a pencil lead, nib or blade. The handle is held near the end between the thumb and middle finger, which acts as a fulcrum about which the instrument may be tilted under control of the index finger, which is held forward of the thumb and middle finger close to the tip so as to allow very fine adjustment.
U.S. Pat. No. 6,793,427 discloses a writing instrument having near its tip an upwardly protruding shaped projection that may serve as a ledge for supporting the index finger.
When performing delicate operations such as cutting, particularly but not only during surgery, very fine control is needed. This is best achieved by holding the instrument as close as possible to the working tip. For example, during surgery better control of a knife or scalpel is achieved by holding the scalpel close to the blade. Often scalpels have a blade attached either fixedly or removably to an elongated handle: it is obvious that it is difficult to control such an instrument if it is gripped remote from the blade just as a pen or pencil cannot be used in a controlled manner if gripped remote from the nib or lead. However, while there is no risk of injury to the user who grips a pen or pencil close to the nib or lead, this is not at all the case with a knife or scalpel having a sharp blade since if the user's finger inadvertently brushes against the blade, there is a significant risk, and even likelihood, of being cut. Not only is this unpleasant for the surgeon, but the possible contamination of the patient by the surgeon's blood is a very severe health hazard to the patient himself.
This risk imposes a limit to the proximity to the blade with which known knives and surgical scalpels may safely be held. Commonly, the handle is shaped for gripping so that the user's fingers are kept well clear of the blade. However, for the reasons stated above this militates against the very fine control of the blade that may be required during surgical operations or delicate craftsmanship, such as paper-cutting and the like.
Cutting operations are not always normal i.e. at an angle of 90° to the surface of a workpiece and it may be necessary to rotate the edge of the blade so as to insert the blade at an angle to the working surface, for example, when cutting a beveled edge. Some knives such as those used for paper cutting, may be equipped with a rotatable tip or tang to which the blade is fixed. However, also in surgical scalpels, there may be a need to insert the blade at an angle to the skin surface and this is difficult to achieve without applying finger pressure against a side surface of the blade, with the attendant risk of injury.
Often accurate cutting of thin sheet material, be it paper, plastic sheeting, skin and the like requires that the material be kept taut during the cutting. Otherwise, there is a risk that the material may buckle or fold, militating against or preventing a straight and accurate cut. Commonly, this requirement is met in practice by the user securing a remote edge of the material with an instrument or with the fingers of the weak hand (i.e. the hand not holding the knife) and exerting a slight pulling force to stretch the material against the direction of the cut, while drawing the blade in the opposite direction with the other hand.
In all these cases, accurate control of the instrument is achieved by manipulating the working tip of the instrument using finger pressure: and this is impractical in known designs of knives owing to the risk of injury.
It has been found that mass of the tool is also an important factor in determining comfort. A typical prior art disposable non-retractable scalpel is formed of plastics and weighs approximately 4 gram. This is very light but susceptible to fracture where the blade is affixed to the tang owing to the very narrow cross-section of the tang. A typical prior art non-disposable and non-retractable scalpel is formed of stainless steel weighing approximately 22 gram or titanium weighing approximately 14 gram, but which is prohibitively expensive. This is much stronger such that the handle is not amenable to fracture during use. However, whereas plastic is resilient and gives slightly when pressure is applied, metal handles are much more rigid and intolerant. Consequently, excessive pressure is applied directly to the blade, which is liable to snap. Furthermore, its weight tends to induce an imbalance when the scalpel is rotated during use since there comes a point where the center of gravity of the knife shifts and causes the scalpel to flip over.
FIGS. 34a to 34c show pictorially different views of a prior art surgical scalpel 80 as disclosed in U.S. Design Pat. No. 589,619 to Wu. The scalpel 80 includes a mount 81 supporting a slotted blade 82 mounted on a flat side surface of the mount and having a shield portion 83 that projects outwardly from a side surface of the mount so as to be perpendicular to the surface of the blade and thus parallel to a workpiece 84. During use, as seen in FIGS. 34b and 34c, the shield portion 83 forms a ledge against which the surgeon's finger rests but owing to the fact that the shield portion 83 projects outwardly in a plane that is orthogonal to the blade 82, it lies transverse to the workpiece 84, which is therefore incapable of exerting a contact force on the shield portion 83. Thus the shield portion 83 serves to protect the surgeon's finger 85, but it does this while maintaining both the shield portion 83 and the finger 85 remote from the workpiece and thereby militates against the very fine control that requires stable support of the scalpel during use.
U.S. Pat. No. 3,974,833 discloses a disposable electrosurgical cauterizer having an elongated hollow metal electrode and suction tube encased in a plastic contoured handle having ridges near the tip of the cauterizer.
DE 202 09 870 discloses a knife with a planar mount having a protrusion that is accommodated within a slot of a blade. A shield slides on the mount and can be moved forward to a position where the blade is concealed and backward to a working position where the blade projects through a slot in the projection. The shield supports a projection which could shield a user's finger.
WO 2004/002335 discloses a scalpel having a blade fixed to an arc-shaped bearing surface provided on the front end of the scalpel handle.
WO 2002/049520 discloses a scalpel handle comprising a first upper curved body anatomically corresponding to the curved direction of the forefinger, and a second underlying body prolonging the first one, having an asymmetrical overturned-saddle shape.
U.S. Pat. No. 5,601,584 discloses a scalpel having an elongated handle from one end of which a cutting blade extends laterally, and a depth-of-cut limiting plate extending laterally from the same end and disposed parallel to and spaced apart from the cutting blade.
US 2008/077146 discloses a surgical tool for cutting the annulus of a spinal disc having a stop surface configured to contact the annulus during cutting to prevent further longitudinal movement of the surgical blade into the annulus, thus limiting the size of the incision.
GB 2 271 738 discloses a releasable grip for a surgical knife having a profiled, releasable gripping portion allowing the thumb, index finger and middle finger to be positioned comfortably and accurately enabling controllable and accurate incisions to be made up to the maximum depths of the usable part of the blade.